L8 - Emerging and re-emerging vector borne and zoonotic diseases

triple threat

human activities (MOH)

environmental deterioration (NEA/PUB)

proximity to animals (SFA/NPARKS)

human - enironment interaction diseases

Legionella
Meliodosis
Helminths
Cholera

Human - animal interaction diseases

Influenza
Nipah
Ebola
Food-Borne
MERS

Environment - human - animal interaction diseases

Dengue
Zika
Malaria
Chikungunya
Yellow Fever

Families of RNA viruses (positive sense)

• Togaviridae - alphavirus genus (Chikungunya)

• Flaviviridae (dengue, zika, yellow fever, japanese encephalitis)

• Coronaviridae - Betacoronavirus genus (SARS, MERS)

• retroviridae

• Picornaviridae

Families of RNA viruses (negative sense)

• Paramyxoviridae - Henipavirus genus (Nipah)

• Filoviridae - Ebolavirus genus (Ebola)

• Rhabdoviridae

• Orthomyxoviridae

• Bunyavitidae

• Reoviridae

Host

An animal or plant in or upon which a parasite lives

Vector

An animal that transmits parasitic microorganisms and the diseases they cause from one host to another

Reservoirs

animate or inanimate sources which normally harbour disease-causing organisms and thus serve as potential sources of disease outbreaks

Flavivirus vectors

dengue - Aedes aegypti and albopictus

zika - Aedes aegypti and albopictus

yellow fever - Aedes aegypti

japanese encephalitis - culex species

west nile - culex species

tick borne encephalitis - ticks

Alphavirus vectors

Chikungunya - Aedes aegypti and albopictus

ross river - Aedes vigilax, aedes camptorhynchus and culex annulirostris

western equine encephalitis - culex species

Dengue and chikungunya transmission cycle

• get bit

• 2-14 days intrinsic incubation

• around 7 days fever - viremia

• get bit again

• 7 days extrinsic incubation (in mosquito)

• mosquito can transmit disease now :(

dengue and chikungunya origin

• sylvatic cycle and urban cycle mixed

• starts in forest

• sylvatic cycle is just mosquitoes and forest

• mosquito transfers ot human (Ae. africanus)

• human transmits to urban mosquitos (Aedes aegypti and albopictus)

• urban cycle begins

Dengue

• single stranded RNA

• flavivirus genus

• 4 stereotypes - evolved from sylvatic viruses that then transmitted to urban cycles

japanese enchephalitis and west nile virus transmission cycle

• mosquito vectors (culex spp)

• animals (birds for both, pigs also form JEV)

• incidental hosts - humans

• dead end virus

dengue global situation

increasing cases

increasing frequency of outbreaks and bigger magnitude

20-40 thousand deaths per year

economic burden dengue

singapore - 2000-2009 estimates $0.85-1.15 billion

41%-58% direct medical and non-medical cost and indirect costs such as loss in work productivity and reduction of household services

the rest in vector control

cambodia - each case typically $30-105

67% of households incurred average debt of $25

food per household per week - $9.5

mosquito environment

• Aedes aegypti - built environment (urban)

• Aedes albopictus - greenery and forest

Global trends that impact dengue

• increas in urbanization - megacities

• increased human density

• migration and change in demographic

• improved travel efficiency

urban populations

60% of global populations expected to live in cities by 2030

urban population increased from 220 million to 732 million between 1900-1950

in 2030 4.9 billion people are expected to be urban dwellers

where will most urban growth occur?

Asia pacific (predicted)

travel out of asia pacific region

2.8 billion journeys today - grow to 6.1 billion by 2034.

half will touch asia pacific region in 2034, up from 40% today

how has global distribution of dengue stereotypes changed?

1970 - only SE had all 4 stereotypes, rest of world only had DEN1 and 2

2009 - more countries have dengue and all 4 stereotypes are found almost everywhere except middle east. (i think - map was not clear)

climate change and vector diseases

VBD’s expand geographical range

shift towards higher elevation - due to general warming temps

reduce high over-wintering mortality of vectors - declining number of cool days

increasing length of transmission season

increasing trend of epidemic potential

• more extreme precipitation

• diminishing snow and glacier covers - higher temps

2 strategies for disease control

• replacement - etablish dominant wolbachia-aedes population that is resistant to infection

• suppression - reduce mosquito population to a level that inhibits disease transmission

project wolbachia stats

430,000 households

35% of households in singapore by 2024

gravitrap success

more than 9-% reduction of aedes aegypti across 5 years

levels of analysis for wolbachia project

• township

• individual - risk to individuals

which disease reduction approach did NEA choose and why

Suppression

• targets mosquito population, doesnt rely on wolbachia

• involves releasing male mosquitos - they dont bite yay

• consistent w singapores public messaging on vigilance regarding mosquito breeding

• release of male mosquitos can be halted at any time - leaves no ecological footprint. replacement can follow if needed

chikungunya virus genotype

• single stranded RNA

• Genus: alphavirus

• 1 stereotype, 3 lineages

• evolved from sylvatic viruses

• 7-20 years between pandemics

• found in west and central eastern Africa and SE asia

chikungunya pandemic 2004-2010

A226V mutation allowed adaptation to Ae. albopictus and also shortened exctrionsic incubation period

moved from kenya to india, sri lanka, maldives, seychelles, reunion island etc.. then thailand, cambodia, malaysia, sg, indonesia

Bat borne viruses

• Ebola virus

• Nipah

• SARS

ebola tranmission dynamics

spillover from other animals, then intra and inter species transmission in bats.

Nipah

started in fruit bats

transferred to pigs

through close contact w infected pigs it spread to humans

Nipah virus bangladesh

date palm sap contaminated w bat excretions - started outbreak in 2011

modes of transmission - Nipah

3 modes:

• contaminated date palm sap

• spillover to another animal (i.e. horses) then human contact with this intermediary leads to infection

• pigs - rapid transmission between pigs - asymptomatic facilitating spread

Coronaviruses - SARS

Singapore 2003

spread to most of asia, north america and europe

casualties of SARS

• Number of cases reported

  • Between November 2002 and July 2003, a total of 8,096
    cases were reported globally. In Singapore, 238 people
    were infected.

• Number of lives claimed

  • Sars killed 774 people worldwide, including China (349
    deaths), Hong Kong (299 deaths), Canada (43 deaths),
    Taiwan (37 deaths) and Singapore (33 deaths)

Bats - SARS and MERS

Bats transmitted to camels like 30 years ago

this then transferred to humans who spread it to populations

rare to have direct transfer from palm civets infected by bats to humans